Containers or tubes of a fuel storage system have been produced from various resin materials, because the weight is reduced; a rust proof treatment is not needed; the freedom of shape is high; the number of processing steps is reduced; and the production process is fully automated. In particular, various automobile parts such as tubes, hoses and fuel-related parts are produced from polyamides such as nylon-11 and nylon-12. The polyamides have been widely used because they are light in weight, free from rust and have a good fuel-barrier property to normal gasoline, thus combining excellent properties required in the application to fuel storage.
In recent requirement in reducing the exhaustion of gasoline sources and protecting the environment, the use of a mixed fuel of gasoline added with an alcohol such as ethanol comes to be considered. However, since polyamides have a considerably low barrier to alcohols, the permeation amount of a mixed gasoline through polyamide reaches as high as 50 to 60 times the permeation amount of a normal gasoline. Therefore, polyamide fails to fully meet the regulations which will be made increasingly strict and a material with a higher barrier is keenly required.
It has been known that the heat resistance of a thermoplastic resin is improved by the addition of a polycarbodiimide (Patent Document 1). It has been also known that the hydrolysis resistance, oil resistance and metal halide resistance of polyamide is improved by the addition of an aliphatic carbodiimide compound (Patent Document 2). However, these patent documents are completely silent about the improvement in the fuel barrier property and mechanical properties such as strength, impact resistance and elongation.    Patent Document 1: JP 02-175757A    Patent Document 2: JP 11-343408A